Title: Degradation behaviour and microstructural characterisation of HVOF-sprayed Cr3C2-NiCr cermet coatings in molten salt environment
Authors: V.N. Shukla; R. Jayaganthan; V.K. Tewari
Addresses: Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee-247667, India ' Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee-247667, India ' Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee-247667, India
Abstract: The present work investigated the cyclic high temperature degradation behaviour of high velocity oxy-fuel (HVOF) sprayed Cr3C2-NiCr coating deposited on 310S stainless steel (310S). The coated as well as uncoated specimens were exposed to molten salt (Na2SO4-60%V2O5) environment at 700°C under cyclic conditions. The kinetics of hot corrosion was established using thermogravimetric technique. The corrosion products were characterised using the techniques such as X-ray diffraction, FE-SEM/EDAX and X-ray mapping for elucidating the corrosion mechanisms. The Cr3C2-25%NiCr coating was found to be successful in maintaining its continuous contact with the alloy substrate during cyclic degradation under simulated laboratory condition. HVOF sprayed Cr3C2-25%NiCr coating on 310S alloy substrate is found to be very effective in reducing the corrosion rate in the aggressive environment at 700°C as observed from the present work. The oxide scales for Cr3C2-25%NiCr coated specimen were found to be intact and spallation-free. The parabolic rate constant of the coated specimen was lower than that of the bare specimen. The better hot corrosion resistance imparted by Cr3C2-NiCr coatings may be attributed to the formation of oxides of chromium, nickel and spinel of nickel and chromium.
Keywords: high velocity oxy fuel; HVOF; Cr3C2; chromium carbide; NiCr; nickel-chromium; hot corrosion; kinetics; oxide scale; degradation behaviour; microstructure; cermet coatings; molten salt; high temperature degradation; Cr3C2-NiCr coatings; stainless steel; simulation; corrosion resistance.
International Journal of Materials and Product Technology, 2016 Vol.53 No.1, pp.15 - 27
Accepted: 24 May 2015
Published online: 26 Mar 2016 *